The present invention relates in general, to substrate coating techniques and, in particular, to a method of producing wear-resistant hard layers of hard metal compounds.
It is known to deposit such layers on substrates by vacuum evaporation or cathode sputtering in a reactive atmosphere while at the same time exciting the reaction gas by an electric gas discharge, to stimulate its reactivity. Such a discharge is present in a cathode sputtering process, and with other evaporation methods, it may be produced by means of suitable electrodes in the evaporation chamber. So called "low voltage arc discharge has proven to be particularly satisfactory for vapor deposition, if too strong a heating of the substrates is to be prevented. That is, due to the particularly strong activation of the reactants in the low voltage arc, and adequate reaction is obtained even on cooled substrates, which frequently is not the case with other methods of ion supported reactive deposition.
In particular, the evaporation of titanium in nitrogen, which results in hard, wear-resistant TiN coatings, is known, Due to the brilliance and golden appearance of such castings, they are used, among others, for pieces of jewelry and utility articles. It is further known to produce wear-resistant coatings by evaporating titanium in acetylene or ethylene while evaporating the titanium by means of an electron beam and using additional electric fields for activating the residual gas atmosphere in the evaporation space. This method, however, has a disadvantage in the relatively high temperature (almost 1000.degree. C.) to which the substrates to be coated, are heated. Many materials do not stand such a temperature so that in such cases the mentioned method cannot be applied.
A similar method relates to cathode sputtering of titanium in hydrocarbons with admixed nitrogen, producing a condensate of a crystalline solid solution of titanium carbide and titanium nitride. Such layers are also hard and abrasion-resistant, however, because of their carbide content they are susceptible to oxidation, particularly if during later use they are exposed to high temperatures as in the case of carbide-tipped tools, for example.